This invention relates generally to substrate handling systems. More particularly it concerns mechanically rotating a substrate stack passing through a document handler.
Electrophotographic printing is a well-known and commonly used method of copying or printing documents. Electrophotographic printing is performed by exposing a light image representation of a desired document onto a substantially uniformly charged photoreceptor. In response to that light image the photoreceptor discharges, creating an electrostatic latent image of the desired document on the photoreceptor""s surface. Toner is then deposited onto that latent image, forming a toner image. The toner image is then transferred from the photoreceptor onto a receiving substrate such as a sheet of paper. The transferred toner image is then fused with the substrate, usually using heat and/or pressure. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the production of another image.
Modern electrophotographic printers often include a finisher. In general, a finisher is a device that does something to substrates carrying a fused image. For example, a finisher might sort multiple copies of a given print job into multiple substrate stacks, add front and back covers to each stack, and then bind the individual substrate stacks together, possibly by stapling, into individual booklets. When used with high volume printers a finisher must quickly complete its task, without jeopardizing stack integrity, and while preserving stack neatness. Complicating finishing processes is a desire to keep the size of the printer as small as possible. A small finisher has only a short distance available to complete its operations. Another problem that complicates finishing is the wide variability of stack sizes. For example, a given substrate stack might consist of only a single, thin sheet of paper while another substrate stack might consist of dozens of relatively thick cardboard sheets.
While prior art finishers have been successful, their limitations have brought on a desire for improved performance. In particular, the need to rapidly rotate a substrate stack to achieve the required orientation for a given finisher operation has become apparent. For example, if a substrate stack could be rapidly rotated a given finisher function could operate on any side of the stack at high speed. For example, if a substrate stack could be rapidly rotated a fixed edge stapler could staple any side of the stack. Therefore, a substrate stack rotating device that is capable of rotating a substrate stack at high speed, in a short distance, with neatness and precision, that is capable of handling variable thickness stacks, and that is low cost would be beneficial.
The principles of the present invention provide for low cost, high-speed rotation of variable thickness substrate stacks in a short distance and with neatness and precision. A substrate stack rotating device according to the principles of the present invention includes a lower rotating disk and an upper rotating disk that are located in a substrate path to receive a moving substrate stack. The upper disk is driven downward such that a substrate stack is pinched between the lower and upper rotating disks. The resultant clamping force helps maintain substrate stack integrity and neatness. Once a substrate stack is clamped, one of the disks is rotated to bring the substrate stack into a desired orientation. The upper rotating disk is then released, the substrate stack beneficially moves away from the disks, and the substrate stack rotating device is ready to accept another substrate stack.